The present invention relates to a semiconductor device which includes a thin film capacitor used in an integrated circuit (IC) or a large scale integration (LSI) circuit.
A conventional semiconductor device of the type described comprises a substrate, a thin film capacitor on the substrate. The thin film capacitor has a lower electrode layer deposited on the substrate, a dielectric layer stacked on the lower electrode layer, and an upper electrode layer overlaid on the dielectric layer. The lower electrode layer and the upper electrode layer are made of a conductive material, such as polycrystalline silicon, or the like. The dielectric layer is conventionally made of SiO.sub.2 or Si.sub.3 N.sub.4 and recently made of (Ba,Sr)TiO.sub.3, Pb(Zr,Ti)O.sub.3, Pb(Mg,Nb)O.sub.3, Pb(Mg,W)O.sub.3, or the like.
A plurality of the thin film capacitors may be arranged on the substrate in the above-mentioned manner, and in this event, each of the thin film capacitors may be identical in structure with one another.
In the conventional semiconductor device, when the dielectric layer of the thin film capacitor is made of the aforesaid (Ba,Sr)TiO.sub.3, or the like, the lower electrode layer is often formed by double layers one of which is made of Pt and another one of which is made of Ta or Ti. The lower electrode is thereafter shaped into a predetermined configuration with a side surface exposed to an atmosphere.
However, the lower electrode layer which includes the aforesaid Ta layer is quickly oxidized from its side surface, while the dielectric layer of (Ba,Sr)TiO.sub.3 or so is being overlaid on the lower electrode layer. The same problem is caused to occur when such a lower electrode layer is subjected to a heat-treatment in an oxygen atmosphere. The oxidization of the lower electrode layer objectionally increases a resistance value of the lower electrode layer. This brings about a serious problem in the case where the thin film capacitor has a small area.
Herein, it is assumed that a semiconductor device comprises a plurality of the thin film capacitors. In this event, the dielectric layer of (Ba,Sr)TiO.sub.3 or so is not only formed on the lower electrode shaped into a predetermined form but also is extended to an area between two adjacent ones of the thin film capacitors. As a distance between two adjacent ones of the thin film capacitors becomes short, a coupling capacity therebetween is increased. An increase of the coupling capacity often gives rise to a wrong operation of the IC or LSI which comprises a plurality of the thin film capacitors.